Self-calibrating temperature probe

Abstract

A probe for measuring the temperature of a substrate in a substrate processing chamber. The probe includes a light pipe, one end of which is inserted into the processing chamber. The other end of the light pipe is connected to a bifurcated optical fiber. A light source is optically coupled to one branch of the optical fiber, and a pyrometer is optically coupled to another branch. To self-calibrate the probe, an object of stable reflectivity, e.g., a gold-plated wafer, is inserted into the chamber, the light source is activated, and the intensity of light reflected from the object is measured by the pyrometer.

What is claimed is: 
     
       1. An apparatus for calibrating a substrate processing system, comprising: an optical guide with an input end and an output end, the input end configured to sample light from a processing chamber that includes a reflector plate, wherein the optical guide extends through a passageway in the reflector plate;   a split optical fiber having a trunk and first and second branches, the trunk optically coupled to the output end of the optical guide;   a light source optically coupled to the first branch; and   a sensor optically coupled to the second branch.   
     
     
       2. The apparatus of claim 1 further comprising a body having a known reflectivity configured to fit in the processing chamber. 
     
     
       3. The apparatus of claim 2 wherein the body rests on the reflector plate. 
     
     
       4. The apparatus of claim 2 wherein the body is suspended above the reflector plate. 
     
     
       5. The apparatus of claim 1 further comprising a controller programmed to derive a temperature measurement from the sensor. 
     
     
       6. The apparatus of claim 5 wherein the controller is programmed to activate the light source and derive the temperature measurement when the light source is activated. 
     
     
       7. The apparatus of claim 6 wherein the controller is programmed to compare the derived temperature measurement to a stored temperature measurement to calibrate the apparatus. 
     
     
       8. A method of calibrating a substrate processing system, comprising the steps of: injecting light from a light source through a first branch of a split optical fiber, a trunk of the split optical fiber optically connected to an optical guide that extends through a passageway in a reflector plate, and through the optical guide into a processing chamber;   reflecting injected light from a reflective body in the processing chamber;   sampling reflected light via the optical guide; and   measuring an intensity of sampled light using a sensor optically coupled to a second branch of the split optical fiber.   
     
     
       9. The method of claim 8 further comprising positioning the body on the reflector plate. 
     
     
       10. The method of claim 8 further comprising suspending the body above the reflector plate. 
     
     
       11. An apparatus for determining a corrected temperature of a body in a substrate processing system, comprising: a first optical guide having an input end and an output end, the input end of the first optical guide positioned to sample light reflected from the body;   a first split optical fiber having a trunk and first and second branches, the trunk of the first optical fiber optically coupled to the output end of the first optical guide;   a first light source optically coupled to the first branch of the first split optical fiber;   a first sensor optically coupled to the second branch of the first split optical fiber;   a second optical guide having an input end and an output end, the input end of the second optical guide positioned to sample light reflected from the body;   a second sensor optically coupled to the output end of the second optical guide; and   a controller programmed to activate the first light source, receive first and second temperature indications from the first and second sensors when the first light source is activated, and derive a temperature correction factor from the first and second temperature indications.   
     
     
       12. The apparatus of claim 11 further comprising a second split optical fiber having a trunk and first and second branches, the trunk of the second optical fiber optically coupled to the output end of the second optical guide, and a second light source optically coupled to the first branch of the second split optical fiber, and wherein the second sensor is optically coupled to the second branch of the second split optical fiber. 
     
     
       13. The apparatus of claim 12 wherein the controller is programmed so that the second light source is not activated while the second sensor generates the second temperature indications. 
     
     
       14. The apparatus of claim 11 further comprising a third optical guide having an input end and an output end, the input end of the third optical guide positioned to sample light reflected from the body, and a third sensor optically coupled to the output end of the third optical guide. 
     
     
       15. The apparatus of claim 14 wherein the controller is further programmed to receive a third intensity indication from one of the first, second, and third sensors when the first light source is not activated, and to derive a temperature measurement from the third intensity indication and the temperature correction factor. 
     
     
       16. The apparatus of claim 15 wherein the controller is programmed to derive the temperature correction factor by using the first and second temperature indications to compute a roughness for the body and using the roughness to compute the temperature correction factor. 
     
     
       17. A method of determining a property of a body in a substrate processing chamber, comprising the steps of: shining light from a light source into a first branch of a first split optical fiber, a trunk of the first split optical fiber optically coupled to a first optical guide;   injecting light through the first optical guide into the processing chamber;   sampling light that was infected through the first optical guide and reflected by the body with the first optical guide;   measuring a first intensity of light sampled by the first optical guide using a first sensor optically coupled to a second branch of the first split optical fiber;   sampling light that was injected through the first optical guide and reflected by the body with a second optical guide;   measuring a second intensity of light sampled by the second optical guide using a second sensor optically coupled to the second optical guide; and   deriving a measurement of the property from the first and second intensities.   
     
     
       18. The method of claim 17 wherein the property determined is roughness. 
     
     
       19. The method of claim 18 further comprising comparing the first and second intensities of light to third and fourth intensities of light previously measured for a substrate of known roughness. 
     
     
       20. The method of claim 17 wherein the property determined is emissivity. 
     
     
       21. The method of claim 20 further comprising comparing the first and second intensities of light to third and fourth intensities of light previously measured for a substrate of known emissivity. 
     
     
       22. A substrate processing system comprising: a reflector plate in a process chamber;   a substrate support to hold a substrate in the chamber so as to form a reflective cavity between the reflector plate and the substrate;   a heater to heat the substrate;   an optical guide having an input end and an output end, the input end of the optical guide extending through a passage in the reflector plate to sample light from the reflective cavity;   a split optical fiber having a trunk and first and second branches, the trunk optically coupled to the output end of the optical guide;   a light source optically coupled to the first branch; and   a sensor optically coupled to the second branch.   
     
     
       23. A method of correcting a temperature measurement of a substrate in a processing chamber, comprising the steps of: inserting a substrate into a chamber;   heating the substrate in the chamber;   measuring a temperature and a roughness of the substrate in the chamber with a plurality of probes; and   using the roughness of the substrate to derive a corrected temperature measurement.   
     
     
       24. The method of claim 23 wherein the roughness is measured by a pair of probes and the temperature is measured with one of the pair of probes. 
     
     
       25. The method of claim 23 wherein the roughness is measured by a first probe and a second probe and the temperature is measured by a third probe. 
     
     
       26. The method of claim 23 wherein the roughness is measured with a first pair of probes, and further comprising generating first and second temperature indications from a second pair of probes, determining a temperature difference between the first and second temperature indications, adjusting the temperature difference by a correction factor that is derived from the roughness of the substrate, and correcting the measured temperature by adding a correction quantity that is derived from the adjusted temperature difference. 
     
     
       27. An apparatus for measuring the temperature of a substrate in a substrate processing chamber, comprising: a light source for injecting light into the processing chamber;   a first probe and a second probe for measuring first and second intensities, respectively, of injected light when the light source is activated;   a third probe for generating a temperature indication when the light source is not activated; and   a controller programmed to activate the light source, to receive the temperature indication from the third probe, to receive the first and second intensities from the first and second probes, to derive a temperature correction factor from the first and second intensities, and to derive a corrected temperature by using the temperature indication and the temperature correction factor.   
     
     
       28. The apparatus of claim 27, wherein at least one of the first and second probes samples light that is injected from another probe. 
     
     
       29. The apparatus of claim 28, wherein the one probe is the first probe and the another probe is the second probe. 
     
     
       30. An apparatus for measuring a property of a body in a substrate processing system, comprising: a first optical guide having an input end and an output end, the input end of the first optical guide positioned to sample light reflected from the body;   a first split optical fiber having a trunk and first and second branches, the trunk of the first optical fiber optically coupled to the output end of the first optical guide;   a first light source optically coupled to the first branch of the first split optical fiber;   a first sensor optically coupled to the second branch of the first split optical fiber;   a second optical guide having an input end and an output end, the input end of the second optical guide positioned to sample light reflected from the body;   a second sensor optically coupled to the output end of the second optical guide; and   a controller programmed to activate the first light source, receive first and second intensity indications from the first and second sensors when the first light source is activated, and derive a measurement of the property from the first and second intensity indications.   
     
     
       31. A method of calibrating a substrate processing system, comprising the steps of: placing a body having a substantially stable reflectivity in a processing chamber;   injecting light from a light source through a first branch of a split optical fiber, a trunk of the split optical fiber optically connected to an optical guide, and through the optical guide into a processing chamber;   sampling light that was injected through the optical guide and reflected from the body via the optical guide;   measuring a first intensity of light sampled by the optical guide using a sensor optically coupled to a second branch of the split optical fiber; and   comparing the first intensity to a second intensity of light previously sampled by the optical guide when the body was in the processing chamber to detect changes in the processing system.   
     
     
       32. The method of claim 31 wherein the processing chamber includes a reflector plate, and the optical guide extends through the reflector plate. 
     
     
       33. The method of claim 32 further comprising positioning the body on the reflector plate to detect changes in the light source, optical fiber, or optical guide. 
     
     
       34. The method of claim 32 further comprising suspending the body above the reflector plate to detect changes in the processing chamber. 
     
     
       35. The method of claim 31 further comprising correcting a measured temperature based on the detected change in the processing system. 
     
     
       36. An apparatus for calibrating a substrate processing system, comprising: an optical guide with an input end and an output end, the input end configured to sample light from a processing chamber;   a split optical fiber having a trunk and first and second branches, the trunk optically coupled to the output end of the optical guide;   a light source optically coupled to the first branch;   a sensor optically coupled to the second branch; and   a controller configured to activate the light source when a body having a substantially stable reflectivity is positioned in the processing chamber and to derive a first intensity of light sampled by the optical guide, to store a second intensity of light previously sampled by the optical guide when the body was in the processing chamber, and to compare the first intensity to the second intensity to detect changes in the processing system.   
     
     
       37. The method of claim 23, wherein measuring the temperature and the roughness of the substrate includes sampling light that was injected through a first probe and reflected by the body with the first probe, measuring a first intensity of light sampled by the first probe, sampling light that was injected through the first probe with a second probe, and measuring a second intensity of light sampled by the second optical probe. 
     
     
       38. The method of claim 23, wherein each probe includes an optical guide with an input end and an output end, the input end configured to sample light from the processing chamber, a split optical fiber having a trunk and first and second branches, the trunk optically coupled to the output end of the optical guide, a light source optically coupled to the first branch, and a sensor optically coupled to the second branch.